1. Field of the Invention
The invention relates to image processing, and more particularly relates to a data transformation device performing discrete cosine transforms and inverse discrete cosine transforms.
2. Description of the Related Art
MPEG-4 is a multimedia video data compression standard. MPEG data is supported by a wide variety of products, including, digital televisions, set-top boxes, digital satellite systems (DSS), televisions, decoders, digital versatile disk players (DVD players), video conferencing apparatuses and web cams among others. MPEG compression reduces file size, thus, less storage is required in the described devices. Moreover, the bandwidth required for transmission of video and image data is reduced.
FIG. 1 is a diagram illustrating a conventional image compression device. The conventional image compression device comprises a discrete cosine transform operator (DCT operator) 13 and a quantizer 14. The DCT operator 13 is configured to perform discrete cosine transforms (DCT). The quantizer 14 is configured to quantize the DCT factors. The conventional image compression device provides a feedback path comprising an inverse quantizer 15, an inverse DCT operator 16, an adder 17, switching logic units 12 and 19, and a subtractor 11. The conventional image compression device is configured with an image memory 18 for extracting a motion vector V. The conventional image compression device further comprises a coding controller 10 for controlling the quantizer 14 and the switching logic units 12 and 19.
The DCT operator 13 can process input image data where the image size is N×N. The DCT process of the conventional image compression device processes and transforms the data by the row-column decomposition method, as shown in FIG. 2. The number of multiplications is reduced by the row-column decomposition method with the property of the DCT kernel. The DCT operator 13 outputs the transformed N.times.N data square to the quantizer 14 subsequent to row-column decomposition.
In the row-column decomposition, the row-direction image data of the N×N image data is first provided to a first direction DCT operate 131. The first direction DCT operate 131 applies the processed row-direction image data row-column decomposition stored in a transportation memory 132. The image data processed by the first direction DCT operator 131 is read in the column-direction and provided to a second direction DCT operator 133 for processing by the second direction DCT operator 133 in the column-direction.
In the row-column decomposition of the conventional DCT calculation, the DCT factors are quantized by the quantizer subsequent to the first and the second direction DCT calculation with the N×N image block by the DCT operator. The dequantizer 15 is enabled subsequent to processing by the N×N image block. After the dequantizer 15 outputs the dequantization result, the inverse discrete cosine transform (IDCT) operator 16 starts the IDCT calculation. The DCT operator 13, the quantizer 14, the dequantizer 15, and the IDCT operator 16 operate, respectively, in the different phases.
In the conventional method, the DCT and the IDCT are applied by the DCT operator 13 and the IDCT operator 16, respectively, thus, higher occupation of a chip area results.